The invention relates to a chemical vapor deposition (CVD) process for coating the insides of hollow bodies, such as flasks, ampoules or the like, with at least one barrier layer, whereby, before the coating phase, i.e., before the coating gas is being introduced into the hollow body, the hollow body is heated in a heating phase using plasma, especially O.sub.2 plasma, to a specified temperature. The invention also relates to a device for carrying out such a process.
Pharmaceutical packing material, such as injection flasks, ampoules or the like, can be provided on the inside with a barrier layer, such that the release of glass components and their transfer into the liquid that is in the packing agent or, in the case of plastic packaging, the penetration of foreign gases, is prevented. Very strict requirements therefore have to be imposed on the quality of such barrier layers. Since the quality of the coating in the coated product cannot be examined or can be examined only with extreme difficulty, the coating process has to be controlled, so that from the process parameters, conclusions can be drawn as to the quality of the coating.
In addition to electrical measuring methods (Langmuir probe for electron and ion properties, mass spectrometry for design and shattering of compounds in gaseous form in plasma), it is known to use optical emission spectroscopy (OES) to study the reactions that occur in a plasma and to control plasma coatings and etchings. OES has the advantage that it works in a "contactless" manner, unlike the other measuring methods, i.e., not in contact with the plasma or tie gas that is to be studied and that thus no harmful interaction with the object to be examined occurs.
"Thin Solid Films" 266 (1995) 8-13 describes that the microstructure and chemical composition of a separated film from the system TiTP/N.sub.2 /N.sub.2 varies owing to the process parameters, whereby the gas composition and cathode temperature can be inferred from the optical emission of the dc voltage plasma.
In conference session 3 "10th International Symposium on Plasma Chemistry" (1991), 2.4-30, the production of La.sub.2 O.sub.3 layers with low C-contamination using HF-plasma-CVD from an organic La compound and oxygen is described, and it is recommended the ratio of intensities of two lines (CO and O.sub.2.sup.4) be used to adjust the vapor pressure of the La precursor to a fixed value, so that a C content of &lt;3% of the layer is ensured.
The book "Plasmatechnik [Plasma Technology]" by Schade, Suchanek and Tiller, published in 1990 by Verlag Technik GmbH Berlin, describes on pages 140 and 141 how the time plot of CO and AlCl emission is used, or in another example, how Si emission is used as a process control during plasma etching. In the latter case, how good or poor etching homogeneity is can be judged from the time plot of the emission line.
EP-0 299 752 indicates a process for monitoring and controlling plasma-CVD coatings. The process lies in the optical plasma emission being measured and spectrally analyzed, and the results in this regard being used to adjust plasma properties to be able to produce, in a reproducible manner, layers with specified properties. The signal that guides the adjustment is the ratio of two or more characteristic lines that are at a fixed ratio to the important plasma parameter electron temperature.
DE-38 30 622 describes a pulsed plasma-CVD process for coating the insides of quartz glass tubes. The specific emission of a layer-forming compound (SiO) is used to adjust the length and position of the plasma area in the tube, which contributes to layer formation, during coating to a specified value.
From DE 4008405 C1 a PCVD process is known for the production of a dome-shaped substrate that is provided on the inside surface and/or outside surface with a dielectric layer system, in which before coating is done, an O.sub.2 gas discharge is ignited to condition the inside surface of the dome that is to be coated. The desired substrate temperature is set by the intensity and duration of the O.sub.2 gas discharge. No indications are made, however, about whether and how the heating phase is monitored to ensure the desired substrate temperature.
None of the known processes, however, takes into consideration the specific requirements that are to be met in coating the insides of hollow bodies.